Absorption and desorption behaviours of ammonia on bis(fluorosulfonyl)amide salts investigated using the pressure-swing method

The absorption and desorption behaviours of ammonia (NH3) on bis(fluorosulfonyl)amide (FSA) salts were investigated using the pressure-swing method. The effects of the cation species and temperature of the four types of FSA single salts (Li[FSA], Na[FSA], K[FSA], and Ca[FSA]2) and (Na, K)[FSA] eutectic melt on the NH3 absorption behaviour were evaluated. FSA salts exhibited large NH3 storage capacities and the NH3 absorption behaviour was affected by the different FSA salt cation species. The NH3 storage capacity increased with decreasing temperature. Although the alkaline metal FSA salts were liquefied by NH3 absorption at 300 K, Ca[FSA]2 remained solid after NH3 absorption at 300 K. Additionally, K[FSA] absorbed a lower amount of NH3 than at 300 K and remained in the solid state after NH3 absorption at 323 K. These results suggest that NH3 molecules were dissolved in the FSA salts, and eutectic compounds were formed by NH3 absorption on the FSA salts. After NH3 absorption, the salts were found to be composed of ammonium (NH4+) cations and amide (NH2−) and imide (NH2−) anions.